Could an earthquake on flat land still kill someone without any buildings/boulders or such near by?

Question

Suppose you were sitting near the epicenter of an earthquake, sitting down on flat land without much else near by, maybe some grass. Is it still possible that say, a magnitude 8 or 9 earthquake would be lethal, assuming you can spread out enough to avoid tipping over and hitting your head?

It seems like the biggest damage in earthquakes comes from buildings, not the ground splitting apart, but it is also possible the terrain itself could warp like an ocean wave several meters I guess. And if a fissure was opening up near someone from the quake's epicenter, would they have time to react and avoid being dropped into it?

Answer 1

Yes, a person in the open sitting on grass could be killed by a magnitude 8 or 9 earthquake, but in the circumstances you describe it would be very unlikely. Not all large earthquakes produce huge rifts on land, but if you were unlucky enough to have one open up beneath you then the chances are you would fall into it. Another danger would be liquefaction. In some places the moisture content of the land is such that although in normal circumstances it is perfectly solid and stable, when subjected to the violent shaking of an earthquake a phenomenon called liquefaction occurs. The ground becomes a sort of quicksand into which buildings can collapse and humans disappear. It is quite rare, however, and fatalities among people are unlikely if they are out in the open where nothing can fall on them, though I dare say a few unlucky ones might have a heart attack. On hard ground,though, even a fit and healthy young person might be severely bruised and shaken in a magnitude 9 quake.

Answer 2

Normally, during an earthquake most deaths occur when people get buried under collapsing buildings. Assuming as in your question, a person was away from anything that could fall on them and didn't fall into a ravine and didn't get swallowed in a newly formed quicksand, it should be possible to survive a mag 9 event.

The biggest danger in this situation will be a result of rapid acceleration, referred to as Peak Ground Acceleration. In recent years the highest recorded ground acceleration during an earthquake was recorded during 2016 event on the South Island of New Zealand with peak values of 3g (30 $\small\mathsf{m/s^2}$).

A healthy person should have no issues surviving acceleration of this magnitude, especially if lying on the ground. This is due to the fact that people are more resilient to acceleration directed from front to back as opposed to from feet-to-head (or other way around). Bruises and (not very likely) broken ribs would be the biggest issues in such a case.